The objective of this research program is to increase our understanding of how the central nervous system controls and coordinates activity in the jaw muscles for the production of complex motor behaviors such as chewing. In humans, single motor unit electromyography will be used to study the function of the muscles of mastication. At various times during the production of precisely controlled voluntary tasks stimuli will be delivered to trigeminal sensory receptors to determine the effects of this peripheral input on the centrally programmed movements. Analysis of recruitment patterns, contractile properties and spike train characteristics of single motor units will be used to determine the mechanisms by which the nervous system codes for the sequence and intensity of contraction of the various muscles of mastication. These techniques will be used as well to determine the role of the nervous system in the establishment of the 'rest' position of the mandible. Patients with the myofascial pain-dysfunction syndrome will also be studied. The characteristics of muscle function established in normal subjects will be compared with those of patients with this syndrome in order to establish the nature of the neuromuscular disorder which leads to the motor disability. Neurophysiological studies will focus on the use of the guinea pig as an experimental model for study of the interaction of the central nervous system pattern generators responsible for producing rhythmic masticatory movements with the reflex effects of peripheral feedback which results from those movements. Intracellular recording in motoneurons which control the muscles of mastication will be obtained during rhythmic masticatory movements and chewing behavior and will permit analysis of inhibitory and subthreshold excitatory events not observable with any other method. This technique is extremely useful in the study of motor control since the membrane characteristics of motoneurons innervating a particular muscle can be observed during the actual performance of behaviors in which that muscle is involved.